The present invention relates to friction clutches in general, and more particularly to improvements in friction clutch assemblies or units of the type comprising a plurality of coaxial friction clutches. Such friction clutch assemblies can be utilized in automotive vehicles and may include a first clutch which is engaged when the operator of the vehicle desires to transmit torque from the rotary output element of the engine (e.g., from the crankshaft) to a driven element (such as a flywheel), and a second clutch which may be incorporated in the flywheel and serves to connect the latter with the input element of a change-speed transmission. In such clutch assemblies, the friction disc of the first clutch is connected with and receives torque from the crankshaft, and the friction disc of the second clutch is connected with and transmits torque to the input element of the transmission. Each friction disc is flanked by a pair of pressure plates, and at least one pressure plate of each such pair is movable axially of the clutches and can be biased to bear against the respective friction disc.
Friction clutch assemblies of the above outlined character were proposed for use in automotive vehicles in order to reduce the fuel requirements of the internal combustion engines. This is to be accomplished by ensuring that, whenever the engine does not drive the vehicle (e.g., during idling, when the vehicle travels downhill or during short-lasting halts of the vehicle in front of a stop sign or traffic light), the torque transmitting connection between the crankshaft of the engine and the flywheel is interrupted and the engine is arrested. The flywheel continues to rotate and the engine is restarted, as soon as the vehicle is set in motion again, by the simple expedient of reengaging the first clutch so that the flywheel constitutes the starter of the engine. In such conventional friction clutch assemblies, the two friction clutches are disengaged or engaged independently of each other, i.e., the assembly comprises or is combined with discrete release means for each of the two friction clutches. Each release means may comprise a linkage which is operated by a pneumatic motor and a release member which effects actual disengagement of the respective friction clutch.
A drawback of the just described conventional friction clutch assemblies is that their clutches are quite complex and expensive as well as that the provision of two discrete clutch release means contributes to the bulk and initial as well as maintenance cost of the apparatus. The release means are sensitive and hence prone to malfunction. The provision of discrete motors for the two release means contributes significantly to the complexity and cost of the assemblies.